Measuring an air conditioner's performance can settle arguments and save service personnel hours of wasted time.
I have stressed in many previous columns that measurement is the basis of all knowledge (Lord Kelvin). Many times, air conditioning performance is a classic, convenient example of an area where measurement skills are woefully underused. I realize that this is the end of the A/C season for many service facilities, but there's no time like the present to emphasize that measuring outlet air temperature is easy and useful.
Recently, during a period of very hot and humid weather, I saw someone in a shop arguing with a customer over an air conditioner that supposedly wasn't performing up to par. Apparently the motorist had already spent a considerable sum to repair the system and wasn't completely satisfied with the results.
I sympathize with motorists here; those Tire Business readers at the service desks out there know it's easy to drop $1,000 or more on air conditioner repairs. It's understandable that many folks who spend that money expect the A/C to turn the vehicle's cabin into a meat locker.
If motorists don't get these results, they expect tire dealers or service shop operators to retest the system. Then an argument may ensue when a competent technician does so and finds nothing wrong with it. Secretly, both the service personnel and the customer may be afraid that this air conditioner's already working as well as can be expected.
Whether you work in the bays or at the service counter, I recommend that you invest in a high-quality pocket thermometer such as the one shown in the accompanying photograph (available from UEI Automotive; [email protected] ueiautomotive.com). These are available from most air conditioning tool and equipment vendors. Wield your thermometer any time a motorist questions A/C performance.
To do this, stand outside and measure ambient air temperature first. Write that value on your notepad. Then get into the vehicle with the customer and write down the temperature of the cabin air. Note that if the car has been sitting in the sun with the windows closed, interior temperatures easily may exceed 110 F to 120 F.
Because they've never been shown an actual measurement, many motorists have no idea how hot-as a matter of fact, dangerously hot-a vehicle's interior can be.
Next, slide the tip of the thermometer into one of the middle air ducts/outlets in the dashboard. Start the engine, turn on the air conditioner and be sure the temperature controls are set to the maximum cold and recirculated air positions.
For the most accurate results, road test the vehicle so normal air flow is going through the air conditioner's condenser in the front of the vehicle. A good working rule of thumb is that above 80 F and 70-percent relative humidity, a properly operating air conditioner should produce outlet air that is 25-35 degrees cooler than the ambient air temperature. The actual numbers vary according to the heat load, the size of the vehicle's interior, etc.
Besides basic experience, you'll find similar numbers in the original equipment auto makers' air conditioner performance charts. Hopefully, these guidelines will save you from retesting or even recharging an air conditioner that's already doing all it can do to cool the customer's car.
Dan can be reached via e-mail at [email protected]